Liquid liquid mass transfer process and apparatus

ABSTRACT

A COMPONENT OF AT LEAST ONE OF TWO IMMISCIBLE LIQUIDS IS TRANSFERRED INTO THE OTHER LIQUID BY INTRODUCING ONE OF THE LIQUIDS (THE &#34;FIRST LIQUID&#34;) ONTO THE SURFACE OF FIBERS EXTENDING GENERALLY LINEARLY ALONG A CONDUIT WITH THE FIBERS FILLING THE CROSS-SECTIONAL AREA OF AT LEAST A PORTION OF THE LENGTH OF THE CONDUIT AND BEING WETTED PREFERENTIALLY BY THE FIRST LIQUID, FLOWING THE OTHER LIQUID (THE &#34;SECOND LIQUID&#34;) THROUGH THE CONDUIT PAST THE FIBERS THEREBY DRAGGING A FILM OF THE FIRST LIQUID ALONG THE FIBERS, COLLECTING THE LIQUIDS IN A GRAVITY SEPARATOR APPOZIMATE THE DOWNSTREAM END OF THE FIBERS AND THEN SEPARATELY REMOVING THE TWO LIQUIDS FROM THE SEPARATOR.

K. E. CLONTS Sept. 11, 1973 LIQUID-LIQUID MASS TRANSFER PROCESS ANDAPPARATUS Filed July 9, 1971 United States Patent Office 3,758,404Patented Sept. 11, 1973 US. Cl. 208-263 4 Claims ABSTRACT OF THEDISCLOSURE A component of at least one of two immiscible liquids istransferred into the other liquid by introducing one of the liquids (thefirst liquid) onto the surface of fibers extending generally linearlyalong a conduit with the fibers filling the cross-sectional area of atleast a portion of the length of the conduit and being wettedpreferentially by the first liquid, flowing the other liquid (the secondliquid) through the conduit past the fibers thereby dragging a film ofthe first liquid along the fibers, collecting the liquids in a gravityseparator approximate the downstream end of the fibers and thenseparately removing the two liquids from the separator.

BACKGROUND OF THE INVENTION The field of art to which the inventionpertains is liquid-liquid mass transfer between immiscible liquids, forexample the removal of acidic compounds carried in a hydrocarbon bycontacting the hydrocarbon with an aqueous solution of caustic.

One conventional way to transfer a component of one immiscible liquidinto another is the dispersion-settling process in which one liquid isdispersed into the other to form an emulsion and then the emulsion isallowed to settle and separate. One situation in which thisdispersionsettling process is used is in the separation of acidicconstituents from cracked gasoline. This gasoline is treated with anaqueous caustic solution, which is immiscible in the gasoline, to removethe acidic matter. conventionally, this treatment consists of dispersingthe aqueous caustic solution in the gasoline to form acaustic'in-gasoline emulsion. The acidic constituents in the hydrocarbonphase present at the interfacial boundary between the droplets ofaqueous caustic and the surrounding hydrocarbon phase will react withthe caustic to form sodium salts. These salts greatly favor the aqueouscaustic solution and will enter the aqueous phase and diffusivelymigrate into the droplets away from the interfacial boundary. After asufficient time has passed for the acidic constituents to move from thehydrocarbons into the aqueous caustic, the emulsion of hydrocarbon andcaustic is placed in a settling tank and the caustic allowed to settleto the bottom.

The efficiency of the mass transfer of the acidic constituents for agiven volume of aqueous caustic is improved by (a) increasing theinterfacial boundary and (b) decreasing the distance through thehydrocarbon phase that the acidic constituents must diffuse to reachthis boundary. This can be accomplished by making the droplets verysmall, but this inreases the energy requirements to create the emulsion.Also, when the droplets are made smaller, the time for them to settle inthe settling tank is increased.

Another type of liquid-liquid mass transfer is described in US. Pat. No.3,351,434 issued Nov. 7, 1967, to P. G. Grimes, etal., for aLiquid-Liquid Two-Phase Contactor in which discs are rotated by a motorbetween two immiscible liquid layers to extract a component from oneliquid into the other. Such a system reduces considerably the problemsof emulsion settling, but it is still not entirely satisfactory.

The present development creates a large interfacial boundary with verylow energy requirements and eliminates the need of waiting for anemulsion to separate.

SUMMARY OF THE INVENTION It is a general object of the present inventionto provide a process and apparatus for liquid-liquid mass transfer whicheliminates the high energy needs sometimes required to create emulsionsand the problems of separating the constituents of the emulsion.

Another general object is to provide such a process in which a componentof one of two immiscible liquids is transferred to the other through aliquid film on fibers which liquid film is dragged along the fibers by aflow of another liquid.

Other and further objects, features and advantages will be apparent fromthe following description of the present invention given for the purposeof disclosure.

The present invention is based upon the discovery that excellent resultsare obtained in transferring a component of one liquid to anotherbetween the first and second immiscible liquids by (a) introducing thefirst liquid onto an upstream surface portion of a plurality of fibersextending generally along and secured in a conduit, the fibers fillingthe cross-sectional area of at least a portion of the length of theconduit and being wetted by the first liquid preferentially to thesecond liquid, (b) flowing the second liquid throuhg the conduit andpast the fibers in a direction from the upstream portion of the fiberstoward a downstream end of the fibers thereby dragging a film of thefirst liquid along the fibers, (c) collecting the liquid leaving thedownstream end of the fibers in a gravity separator approximate thedownstream end of the fibers, and (d) separately removing the twoliquids from the separator.

With the fibers being preferentially wetted by the first liquid(sometimes herein called the constrained phase), the movement of thesecond liquid (sometimes herein called the continuous phase) through theconduitvwll cause the first liquid to form a film on the fibers and thenmove the film in a downstream direction in the conduit. Because theliquid film on a fiber will completely surround the fiber, this film isheld to that fiber by both the wetting action (adhesion) and the surfacetension around the curvature of the fiber. This reduces considerably thetendency of the liquid film to come free from the fiber and be dispersedin the continuous phase when compared to what occurs with a film on afiat surface such as a disc.

As the film of the constrained phase is dragged downstream along thefibers by the continuous phase, the interface between the two liquids isconstantly changed, thereby increasing the rate of transfer of acomponent between the two liquids.

A gravity separator is placed approximate the downstream end of thefibers so that the liquid film passes from the fibers immediately intothe gravity separator and is collected prior to it becoming dispersed inthe continuous phase.

The component that is transferred between the liquids may be transferredeither into or out of the liquid film on the fibers. The transfer may bethe result of a chemical reaction at the interface such as the removalof acidic constituents of a hydrocarbon by reaction with a base in anaqueous solution or the transfer may be Without a chemical reaction,such as by absorption from one liquid to another.

The fiber should be a material which will not contamimate the process orbe destroyed by it, such as by corrosion. Glass fibers are presentlypreferred for most applications. However, in applications in which theconstrained phase is an aqueous solution of sodium hydroxide and thecontinuous phase is gasoline containing acidic constituents, steelfibers are preferred over glass fibers because the latter will bechemically attacked.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a schematic illustrationof a presently preferred apparatus which can be used with the process ofthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, aconduit has in it a bundle of elongate glass fibers 12 filling theconduit 10 for a portion of its length. These glass fibers 12 aresecured to a tube 14 at a perforated node 16. The tube 14 extends beyondone end of the conduit 10 and has in it a metering pump 18 which pumpsthe first liquid through the tube 14 and onto the fibers 12.

Connecting with the conduit 10 upstream of the node 16 is an inlet pipe20 having in it a metering pump 22. This pump 22 supplies the secondliquid through the inlet pipe 20 and into the conduit 10.

At the downstream end of the conduit 10 is a gravity separator orsettling tank 24 into which the downstream end of the fibers 12 extend.In an upper portion of the gravity separator 24 is an outlet 26 for oneof the liquids and at a lower portion an outlet 28 for the other liquidwith the level of the interface 30 between the two liquids beingcontrolled by a valve 32 in an outlet line 28 acting in response to aliquid level controller indicated generally by the numeral 34.

In operation of the apparatus of this drawing, liquid, such as a causticaqueous solution, is introduced through the tube 14 and onto the fibers12. Another liquid, such as gasoline containing acidic constituents, isintroduced into the conduit 10 through the inlet pipe 20. The fibers 12will be wetted by the aqueous caustic solution preferentially to thegasoline mixture. The aqueous caustic solution will form a film on thefibers 12 which will be dragged downstream through the conduit 10 by thepassage of gasoline mixture through the same conduit. Both liquids willbe discharged into the separator 24 but with the volume of the gasolinebeing greater because the aqueous caustic will move at a slower velocitythan the gasoline. During the relative movement of the gasoline withrespect to the aqueous caustic film on the fibers, a new interfacialboundary between the gasoline and the aqueous caustic solution iscontinuously being formed, and as a result fresh aqueous causticsolution is brought in contact with this surface and allowed to reactwith the acidic content of the gasoline.

In the separator 24, the aqueous caustic solution will collect in thelower portion as it is heavier than the gasoline. The interface 30within the separator 24 is normally kept at a level above the bottom ofthe downstream end of the fibers 12 so that the aqueous caustic film canbe collected directly in the bottom of the separator without it beingdispersed into the gasoline.

Set forth hereafter are various examples illustrating the process of thepresent invention.

EXAMPLE 1 Numerous tests were run with approximately 96,000 glass fibers12 inches in length in a A-inch I.D. glass tube. Two liquids were movedto this tube with the constrained phase being the reaction products of a30% by weight sodium hydroxide aqueous solution and sufiicient cresylicacid to react with half of the sodium hydroxide. The continuous phasewas a mixture of heptane isomers containing about 0.1% phenol. The glassfibers were wetted by the caustic solution preferentially to theheptane.

The caustic solution was introduced onto the upstream end of the glassfibers at various rates between and 60 ml. per hour. The heptanes wereintroduced into the cond it and flow d pa t the fibers at ra es varyingbetween about 210 and 3540 ml. per hour. After passing through the glasstubing, the heptanes were analyzed for phenol content and the resultsshowed the following percent phenol recovery.

Heptanc Caustic Heptanc Percent rate rate, to caustic phenol n11./ml./hr. ratio recovery Run number:

These recoveries are considerably higher than the recovery performancesknown to applicant for similar phase ratios in the dispersion-settlingprocess described earlier herein. Additionally, contamination ofgasoline by sodium ions is much less in the present process than in thedispersion-settling process.

EXAMPLE 2 This was similar to Example 1 except that the fibers wereapproximately 6,700 steel fibers. Excellent percentages of phenolrecovery were obtained here also.

EXAMPLE 3 This example shows an alkylation by transfer of an acid, whichmay be either H or HF in excess of concentration, into a mixture ofsaturated and unsaturated aliphatic hydrocarbons. In this example, theconduit was a 0.3-inch I.D. stainless steel tube containingapproximately 160,000 strands of glass fiber 12 inches long. Thecontinuous phase was a 12 to 1 solution of isopentane to isopentene andthe constrained phase was 98% H 50 Because of the heat generated by thealkylation reaction, both the hydrocarbon feed and the tube were cooledby 0 C. aqueous glycol solution so that the average temperature in thetube during the alkylation reaction was about 11 C. The continuous phaseflowed past the fibers carrying with it the film of the constrainedphase at various rates to give the following alkylation results.

Approx.

Acid percent Hydrocarbon flow, conversion flow, mL/hr. mL/hr. of penteneDuring alkylation, both of the adiphatic hydrocarbons in the continuousphase diffuse through the interface into the acid film where they reactwith each other and then the reaction products diffuse back into thecontinuous phase.

EXAMPLE 4 liquids were flowed through the conduit at various rates offlow and phase ratios with the following results:

From the foregoing discussions, examples and description of theinvention, it is apparent that the objects set forth herein as well asothers have been achieved. Those skilled in the art will recognize thatthe principles of this invention may be applied in several ways, only afew of which have been exemplified herein specifically. Accordingly, theinvention is to be limited only by the spirit thereof and the scope ofthe appended claims.

What is claimed is:

1. In a process for transferring a component of one liquid to anotherbetween contacting first and second immiscible liquids, the improvementcomprising:

(a) introducing the first liquid onto an upstream surface portion of aplurality of fibers extending generally linearly along and secured in aconduit, the fibers filling the cross-sectional area of at least aportion of the conduits length and being wetted by the first liquidpreferentially to being wetted by the second liquid,

(b) flowing the second liquid through the conduit and past the fibers ina direction from the upstream portion of the fibers toward a downstreamend of the 6 fibers thereby dragging a film of the first liquid alongthe fibers and transferring said component between said liquids,

(c) collecting the first liquid leaving the downstream end of the fibersin a gravity separator approximate the downstream end of the fibers, and

(d) separately removing the two liquids from the gravity separator.

2. The process of claim 1 in which the fibers are selected from thegroup consisting of glass fibers and steel fibers.

3. The process of claim 1 in which the first liquid includes a base inaqueous solution and the second liquid includes a liquid hydrocarbonwith an acidic component.

4. The process of claim 2 in which the first liquid includes a base inaqueous solution and the second liquid includes a liquid hydrocarbonwith an acidic component.

References Cited UNITED STATES PATENTS 3,617,531 11/1971 Schlicht 2082632,605,212 7/ 1952 Lobban 208-263 2,701,783 2/1955 Long et al. 208-2633,351,434 1/1967 Grimes et al. 233l0 FOREIGN PATENTS 618,045 4/1961Canada 208263 DELBERT E. GANTZ, Primary Examiner I. M. NELSON, AssistantExaminer U.S. Cl. XR. 2l04l

